Nearly 50 years after a human first set foot on the moon, maybe it's time for a new challenge in space. How about finding out — in our lifetimes — if there's life on planets orbiting our nearest star neighbors?

That's the goal of a project called Breakthrough Starshot — the brainchild of a Russian billionaire, a former director of NASA's Ames Research Center and a group of high-level physicists and engineers.

They hope to send hundreds of tiny spacecraft to the Alpha Centauri star system, where they'll examine planets for signs of life. It's a monumental engineering challenge that will require huge leaps in technology for spacecraft design, propulsion and communication. The attempt by SpaceX and Tesla Chief Executive Elon Musk to get humans to Mars looks like a neighborhood stroll by comparison.

But if Breakthrough Starshot succeeds, we could get snapshots of the Alpha Centauri solar system 4 light-years away — roughly the same as 6,800 trips to Pluto — 30 to 40 years from now. And maybe we'll get a better idea about just how rare life is in the universe.

"This is addressing one of humanity's fundamental questions: Are we alone?" says Breakthrough Starshot Executive Director S. Pete Worden, who ran the NASA Ames center in Mountain View, California, for nine years. "If we find a life-bearing planet orbiting nearby stellar systems, that's one of the most fundamental discoveries of all time."

Starshot isn't the kind of space mission you're used to. It won't use a mammoth rocket to propel a heavy spacecraft. NASA's New Horizons interplanetary probe weighed a bit more than a half ton, for example. Instead, Breakthrough Starshot plans to use a giant Earth-based laser array to shoot a fleet of nearly weightless spacecraft traveling much, much faster. The spacecraft could be just 3 to 12 feet across and weigh as little as a thimbleful of water.

How much faster will they travel? A Starshot spacecraft could move at a fifth the speed of light — 134 million miles per hour — to get to the three stars of the Alpha Centauri system in just over 20 years. Once there, they'll whiz right through, snapping photos furiously, then sending us the data from the far side of the trip.

In comparison, New Horizons took nine and a half years to reach Pluto.

You could argue the Starshot idea came from famous 16th century astronomer Johannes Kepler, who wrote in a letter to fellow brainiac Galileo Galilei, "With ships or sails built for heavenly breezes, some will venture into that great vastness."

If the dinosaurs had a giant laser, maybe they'd still be here.

S. Pete Worden

Starshot's technology started to become practical in 1962, shortly after the invention of lasers. That's when physicist Robert Forward proposed propelling spacecraft by beaming laser light at a reflective sail. Lightsails were tested in our solar system eight years ago with Japan's Ikaros spacecraft, though the sun's light provided only a modest tenth of a G of thrust.

What makes Starshot a compelling idea now is decades' worth of work miniaturizing electronics for computers and smartphones. Starshot plans a "nanocraft" whose mass is about a single gram, the same as a paper clip. That could be enough for the sail, cameras and sensors. These sensors could measure magnetic fields that shield planets from radiation, and they could detect particular wavelengths of light that may indicate the presence of life.

The Starshot nanocraft, like this tiny Earth-orbiting, satellite-on-a-chip called KickSat, will have to carry sensors, a computer and laser — all with about the same mass as a paper clip.

Zac Manchester

Starshot researchers have a specific destination in mind: an actual planet in the relatively balmy habitable zone around Proxima Centauri, one of the three stars in the Alpha Centauri system. Detailed destination plans will evolve as an actual launch date nears.

The Starshot plan initially called for a tiny package of electronics attached to a flat lightsail, perhaps 1 to 4 meters across. Researchers now favor a new idea: a comparably sized spherical lightsail studded with electronics.

Think of it as a large pingpong ball with computers and cameras pointing in different directions. The big advantage? The spherical shape, coupled with a "hollow" laser beam that's stronger toward its outside edge, could be naturally centered on the beam throughout the acceleration.

A photon beam shot from Earth will push the Starshot spacecraft past the moon's orbit in moments.

Darius Farraye/CNET

Starshot's laser gets around a big problem with the rockets we've been using to explore space. Rockets carry their own fuel, so they're really heavy. Imagine you're driving 6,000 miles across the USA and back with no gas stations. Even averaging 30 miles per gallon, you'd need a 200-gallon tank that'll saddle your car with more than 1,200 pounds of fuel. No more jackrabbit starts when the light turns green.

Starshot dispenses with all that because a mothership orbiting Earth would release the nanocraft. The laser hitting the crafts' lightsails will then send them speeding toward Alpha Centauri.

"The beauty of using a photon beam from Earth is the spacecraft has no fuel at all," says George Sowers, a Colorado School of Mines professor who previously was chief engineer for the Atlas V rocket that launched New Horizons. A laser launch frees you from "the tyranny of the rocket equation," he says.

The Starshot laser system, concentrating gargantuan amounts of light onto a tiny craft for just a few minutes, could accelerate the nanocraft with a 60,000-G force. (The Earth pulls you to the ground with a force of 1G.) That's the same as a bullet shot from a gun, but protracted for minutes instead of a split second. Afterward, the nanocraft would be six times the distance from the Earth to the moon and traveling far faster than anything else humans have ever built. If you could fly a plane at that clip, you'd circle the Earth's equator in two-thirds of a second.

The project has begun funding researchers to hone physics possibilities into engineering realities. Both Worden and Avi Loeb, leader of Harvard's Astronomy Department and the Breakthrough Starshot Advisory Committee, point to three big problems the team needs to solve before any nanocraft can wing their way through space.

The first is building an array of lasers that are powerful enough, cheap enough and intimately interlinked so millions can act like a single laser. The combined laser power needs to be something close to 100 gigawatts, the output of about a 100 nuclear power plants, though only for a short burst.

Fortunately, lasers are becoming more economical. "Laser power is doubling every 20 months and the cost is halving every 34 months," Loeb says. Even so, you can expect the laser array to cost something like $10 billion, Loeb says.

Once launched into space, the Starshot nanocraft will inflate a 1- to 4-meter spherical lightsail that will be sent speeding off toward Alpha Centauri when hit by a laser beam from Earth.

Darius Farraye/CNET

The second challenge is building a lightsail material that won't vanish into a puff of ash when hit by that humongous laser beam. "Even if one-ten-thousandth of the laser energy is absorbed, it'll burn," Loeb says.

Third is finding a way for the nanocraft to send a message back to Earth with a low-power laser. Starshot researchers believe the same laser array that accelerates the nanocraft can work in reverse to receive a returning laser signal — a difficult feat since the nanocraft's signal will be weak after traveling such a vast distance.

Starshot this year began funding research projects to solve the challenges, Manchester said. It's awarded its first grants for high-powered laser research, and now it's asked for materials science projects on crafting light sail that's extremely light and extremely reflective.

Manchester himself has some experience in extreme spacecraft. He's the leader of a project called KickSat that's launched into Earth orbit one batch of teensy satellites -- they look like naked circuit boards about the size of a large postage stamp -- and plans another launch of new KickSat-2 models this November.

"The fact that we built 4-gram satellites and flew them in space -- that lends some credibility to the [Starshot] story," Manchester said. "It's a stepping stone."

KickSat-2 satellites cost just $20 apiece. Starshot's nanocraft won't be that cheap, but they'll still be affordable enough that we can launch them in droves from a single mothership. That'll give us lots of chances to hear messages.

"Once you have the infrastructure, you can launch one per day," Loeb says. "There could be hundreds or thousands of them sent in different directions."

Those are just the three biggest hurdles. The Starshot team keeps tabs on more than two dozen other challenges, too. One is interstellar dust.

Running into even a single hydrogen atom is a big deal when you're tooling along at a fifth of the speed of light. "Think of it as a tiny nuclear bomb hitting you," Loeb says.

The nanocraft could actually harness that energy by exploiting the temperature difference between the front of the spacecraft, where the dust hits, and the cooler backside. Spacecraft and gas pipeline sensors already use this technology, called a thermoelectric generator.

This is addressing one of humanity's fundamental questions: Are we alone?

S. Pete Worden

Breakthrough Starshot also has to wrestle with the political complications of operating a laser powerful enough to vaporize a communications satellite. Worden expects an international coalition would be in control, with any country able to veto a laser shot that could harm aircraft and satellites.

The researchers are also considering the possibility that Starshot could actually announce our existence to potentially hostile aliens.

"I started life [as] a military officer. Usually before you send a mission, you try to figure out ahead what's there," says Worden, previously a brigadier general in the US Air Force who worked on space and missile programs.

Still, even advanced aliens would struggle to catch a tiny nanocraft blasting past at a fifth the speed of light. Humans certainly couldn't handle any alien nanocraft sent here. "These could be flying through the solar system all the time and we'd never see them," Worden says.

Planning an effort that'll cost billions of dollars and take decades to complete might seem like a stretch. The US has struggled to match the massive, sustained effort of the Manhattan Project to build the first atomic weapons or the Apollo program to send humans to the moon. But there have been other large-scale successes.

Traveling to Alpha Centauri is roughly the same as 6,800 trips to Pluto.

Darius Farraye/CNET

The Large Hadron Collider (LHC), an enormous particle accelerator near Geneva but run by scientists from around the globe, found the previously elusive Higgs boson in 2012, thereby advancing our knowledge of the most fundamental physics. Construction on the world's largest and most powerful particle collider began in 1998.

And NASA's Voyager 1 and 2 probes, launched in 1977, are expected to keep gathering scientific data through at least 2025.

Starshot has an interesting difference from some of those other projects: private funding. The program's first $100 million comes from Yuri Milner, a Russian who studied theoretical physics before becoming an investor who did well by plowing money into companies like Facebook, Twitter, Airbnb, Spotify and Alibaba. That may help Starshot avoid the fate of the Superconducting Supercollider, a particle accelerator that might have found the Higgs boson if Congress hadn't famously pulled funding in 1993.

Worden envisions government help from around the world to build the full Starshot program, but 21st century philanthropy could still be important. After all, Facebook Chief Executive Mark Zuckerberg is on the Starshot board, Microsoft co-founder Bill Gates is spending his fortune fighting diseases, Google co-founder Sergey Brin helps sponsor Breakthrough's $3 million annual prizes to scientists and mathematicians, and Amazon CEO Jeff Bezos is plowing millions into his Blue Origin rocket startup.

Just like the space race in the 1960s drove US technology, Starshot could deliver more than just snapshots from Alpha Centauri.

Starshot's researchers are particularly struck by the idea of using the laser to propel heavier objects shorter distances.

"That laser system would totally change the game for solar system transportation and let us get to Mars super quickly and regularly," Stanford's Manchester says.

Governments might be happier coughing up billions of dollars for Starshot's laser if it could be used to push asteroids off collision courses with Earth, too. "If the dinosaurs had a giant laser, maybe they'd still be here," Worden says.

It's years too soon for bean counters to plan any returns on investment, but if Starshot overcomes its enormous challenges, it'll powerfully boost humanity's enthusiasm for space, Sowers says.

"We could get something back that would really inspire people," he says. "It would be incalculable."

First published Aug. 22, 5 a.m. PTCorrection, Aug. 23, 9:32 a.m.: It would take about 100 nuclear power plants to generate power equivalent to that of the launch laser. The number was misstated in the original version of this story.